It has been proposed to make beam steering devices and Fresnel lenses using nematic liquid crystal cells that are dynamically controlled by a control electric field and have separated element zones. These devices have spatial variations in the index of refraction due to the spatial variations in liquid crystal molecular orientation. This creates a spatial variation in the optical phase delay that can provide beam steering devices and Fresnel lenses. Liquid crystal beam control devices are known in the art.
Such devices typically use patterned electrodes over a liquid crystal cell to create a spatial variation in the index of refraction that is useful to control a beam. To keep voltages low, electrodes can be placed on the cell substrates on the inner side or sides. To increase optical performance, the size or aspect ratio of beam shaping elements defined by the patterned electrodes can be small. To provide a device with a large aperture, many beam steering elements are arranged together, much like a Fresnel lens or beam steering device. With liquid crystal beam steering devices, the boundaries between adjacent beam steering elements can take up a large portion of the aperture, for example up to 50%, because the liquid crystal orientation changes by almost 90 degrees from one side of the boundaries to the other.
Unlike physical (fixed) Fresnel lenses or beam steering devices where there can be an abrupt change in the refractive properties at the boundary between different sections (herein referred to as “micro elements” with the understanding that the sections or micro elements are not necessary limited to very small dimensions), in the case of an electric field control over the orientation of liquid crystal molecules, it is difficult to have an electric field that can cause an abrupt change in the orientation of the liquid crystal molecules. This results in a substantial portion of the aperture of the optical device not being able to contribute to the desired optical operation of the device. This portion can be termed a “fly-back” portion or a non-linear zone (NLZ).
Various problems also exist, including the extent of the angular control, the quality of the beam intensity distribution, cost of manufacture, voltage of operation, etc. When the boundaries between the neighboring micro elements are not properly controlled, the useful portion of the optical device is reduced by boundary areas of improperly controlled liquid crystal.